The world's next major crisis will be a lack of water for home use, including drinking water, many scientists predict. Humans can survive around 40 days without food, but much less than that without water to drink.

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The scarcity of water for domestic use is becoming a critical problem, especially in rural parts of developing countries. Surface water in rivers, streams or lakes, and groundwater, are increasingly becoming contaminated with pollutants from factories, households, farms and mines. Wells dug deeper to extract groundwater are drying up.

To meet the water demands of an exploding population, it is time to look up to the sky for the solution: harvesting rainwater as it falls.

As well as for drinking, rainwater serves various needs. It can be used domestically, for example to wash clothes, flush toilets and to water plants, and in the community, for instance in firefighting or to clean public places such as markets, and for agriculture.

If properly done, "rainwater harvesting appears to be one of the most promising alternatives for supplying freshwater in the face of increasing water scarcity and escalating demand", according to the UN Environment Programme. Water catchments, whether it is just small ponds or large dams, can also be used for flood control.

Harvesting rain for domestic use has age-old roots. Ancient Romans used their villa courtyards to collect rainwater that was then stored in large underground cisterns.

Rainwater harvesting in Asia can be traced back to about the ninth century, when the small-scale collection of rain from roofs and simple dams began in rural parts of South and South-East Asia.

Today, rainwater harvesting is commonly practised in parts of East Africa, central Australia and Central America, as well as in Japan, Mexico, Singapore and Thailand, among others.

Countries in South-East Asia and the Pacific enjoy abundant rainfall spread fairly evenly throughout the year, albeit with peaks during the monsoon season that normally occurs between July and December. Annual rainfall in the region typically ranges between 1,500 and 2,500 millimeters, although mountain areas have in excess of 4,000 millimeters. Such massive downpours often cause flooding in lowland areas.

The monsoon season is obviously the peak time for water harvesting. It makes sense for the region to consider widespread, systematic harvesting of rainwater for domestic, agricultural and industrial uses.